Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-1

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-4

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-9

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-9

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Data Type:	xbrli:stringItemType
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Period Type:	duration

Commitments and Contingencies - Ownership and Operating Interest Percentage (Details) - Colstrip [Member]	Mar. 31, 2024	Jan. 16, 2023
Avista [Member] \| Unit 3 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	15.00%
Avista [Member] \| Unit 4 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	15.00%
PacifiCorp [Member] \| Unit 3 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	10.00%
PacifiCorp [Member] \| Unit 4 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	10.00%
PGE [Member] \| Unit 3 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	20.00%
PGE [Member] \| Unit 4 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	20.00%
PSE [Member] \| Unit 3 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	25.00%
PSE [Member] \| Unit 4 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	25.00%
NorthWestern [Member] \| Unit 4 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	30.00%	15.00%
Talen [Member] \| Unit 3 [Member]
Loss Contingencies [Line Items]
Owners percentage interest	30.00%